DEV: Don't user before(:all)/after(:all) (#13389)

Leaking state and non-obvious order (before :all runs *before* RailsHelper.test_setup) are not worth it.
A replacement PR for #13370. Fixes some flaky specs, e.g.
```
bin/rspec './spec/components/freedom_patches/translate_accelerator_spec.rb[1:3]' './spec/jobs/clean_up_user_export_topics_spec.rb[1:1]' --tag ~type:multisite --seed 35994
```

Also included:
* DEV: No need for locale reset (we do it anyway in rails_helper in `test_setup`)

spec/components/theme_settings_parser_spec.rb

@@ -4,7 +4,7 @@ require 'rails_helper'
 require 'theme_settings_parser'
 
 describe ThemeSettingsParser do
-  after(:all) do
+  after do
     ThemeField.destroy_all
   end